Collagens are instrumental in tissue development in the embryo, and in tissue structure and function in the adult. Although the properties of the more prevalent types have been well-studied, recently identified nonfibrillar collagens, like type XIX, are at initial stages of characterization. Type XIX collagen, discovered from rhabdomyosarcoma (RMS) clones, consists of a 268-an amino-terminal domain, an 832-an five-subdomain collagenous region, and a 1 9-an carboxy peptide. Ten cysteines are distributed in the amino-terminus, two in a non-collagenous central segment and two in a conserved carboxy Cys-(Xaa)4-Cys motif found in seven collagen types. Type XIX domain-specific antibodies have identified 1 65-kDa disulfide-linked chains, and immuno-histochemistry has revealed a widespread basement membrane zone (BMZ) localization in adult human tissues. Despite this distribution, type XIX expression in vitro seems restricted to RMS cultured cells which, when induced to differentiate, exhibit dramatic up-regulation of type XIX. Accordingly, transient expression of the mouse XIX transcript in embryogenesis closely parallels that of an upstream muscle regulatory factor (MRF). This proposal is designed to establish the supramolecular structure, biosynthetic properties, and role of type XIX in in vivo pathologic processes associated with myogenic differentiation. Native type XIX will be purified from human umbilical cord by affinity chromatography for ultrastructural examination to test the hypothesis that its supramolecular organization depends upon formation of covalently linked amino-terminal dimers. Biochemical studies of newly synthesized type XIX will define the secretory properties, posttranslational modification, chain composition and disulfide linkages of the "central- and carboxy-cys" using miniprotein constructs. Studies of type XIX in in vivo models of myogenesis are expected to show its induction early in this process together with MRFs. The presence of type XIX in RMS tumors will determine if it is preferentially expressed by the embryonal variant, potentially leading to development of a diagnostic marker for this childhood sarcoma. A mouse denervation model will also be utilized; new data reveals high levels of type XIX in the involved muscle only upon injury, in situ hybridization will be employed to discover if type XIX is expressed by activated satellite cells concomitantly synthesizing MRFs. Immunolocalization will elucidate the deposition of type XIX presumably at the neuromuscular junction, thereby suggesting that it may function as a prominent component of a specialized BMZ important for myoblast migration. The experiments proposed here will significantly advance understanding of a collagen manifested in seemingly different roles in adult tissue BMZ, and in the myogenic pathway evidenced in RMS and muscle regeneration.